1. Field of the Invention
The present invention relates to automated monitoring of the condition of medium and high voltage cables and insulators in an electrically noisy environment, and more particularly, to alternating current (AC) power line discharge. The present invention is particularly advantageous in a case where a power line communications infrastructure is available to carry monitoring data to a central location.
2. Description of the Related Art
Partial discharge (PD) is a phenomenon that occurs in insulation that has sustained damage, such as through aging, physical damage, or exposure to excessively high electric fields. PD may afflict cables, connectors, surge arrestors, and other high voltage devices. Faulty overhead insulators may also generate noise with frequency and phase characteristics similar to PD. PD generates short pulses, whose duration is in the nano-second range or shorter. PD pulses tend to occur at certain phases of an AC power voltage, and tend to be roughly synchronized with the power frequency or twice the power frequency. PD is a member of a class of noise known as line-synchronized noise or line-triggered noise. PD pulses have a continuous broadband spectrum spanning at least a range between kilohertz and hundreds of megahertz.
Many techniques exist for sensing and identifying signals generated by PD on a power line, and for providing an indication of the location of the PD source. For example, Boggs, S. A., The Case for Frequency Domain PD Testing in the Context of Distribution Cable, IEEE Electrical Insulation Magazine, Vol. 19, No. 4, July-August 2003, describes a method for PD detection in the frequency domain, in which the frequency axis is synchronized to a phase of a power voltage on the power line.
These techniques are generally employed after a cable is suspected of PD, and may not be practical for permanent deployment, due to lack of an ability to readily communicating the information to some central location or due to excessive cost. A disadvantage of some of these techniques is their requirement that PD signals be the strongest signals present, and so, such techniques may not function well in a field environment that includes strong radio signals that are picked up by the cable. The radio signals and other forms of external interference are termed “ingress.”